CELL STRUCTURECELL STRUCTURE

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Early daysEarly days

Hans and Zacharias Janssen of Holland Hans and Zacharias Janssen of Holland in the 1590’s created the “first” in the 1590’s created the “first” compound microscopecompound microscope

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1665 - Robert Hooke 1665 - Robert Hooke discovered and described discovered and described the fundamental unit of all the fundamental unit of all living things (cells) by living things (cells) by examining thin slices of corkexamining thin slices of cork

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1674 - The first man 1674 - The first man to witness a live cell to witness a live cell under a microscope under a microscope was Anton Van was Anton Van Leeuwenhoek, Leeuwenhoek, describing the algae describing the algae SpirogyraSpirogyra and named and named the moving organisms the moving organisms animalcules, meaning animalcules, meaning "little animals" "little animals"

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1838 – Matthias Schleiden suggested that 1838 – Matthias Schleiden suggested that all plants are made of cellsall plants are made of cells

1839 – Theodor Schwann suggested the 1839 – Theodor Schwann suggested the same for animalssame for animals

General General cell theorycell theory emerged: emerged:

““the basic unit structure and function of all the basic unit structure and function of all living organisms is the cell”living organisms is the cell”

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1855 – Rudolph Virchow’s theory: “all cells 1855 – Rudolph Virchow’s theory: “all cells arise from pre-existing cells by cell arise from pre-existing cells by cell division”division”

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Unit of Measurements in Cell Unit of Measurements in Cell StudiesStudies

metremetre mm = 1 m= 1 m

millimetremillimetre mmmm = 10= 10-3-3 m m

micrometremicrometre µmµm = 10= 10-6-6 m m

nanometrenanometre nmnm = 10= 10-9-9 m m

picometrepicometre pmpm = 10= 10-12-12 m m

angstromangstrom AA = 10= 10-10-10 m m (obsolete)(obsolete)

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Magnification and Magnification and ResolutionResolution

Magnification Magnification

- the number of times larger an image is - the number of times larger an image is compared with the real size of the objectcompared with the real size of the object

- magnification = size of image- magnification = size of image

actual size of specimenactual size of specimen ResolutionResolution

- the ability to distinguish between two - the ability to distinguish between two separate points separate points

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The Microscope in Cell The Microscope in Cell StudiesStudies

2 different types of microscopes:2 different types of microscopes:

i)i) light microscopelight microscope – uses light – uses light as a source of radiationas a source of radiation

ii)ii) electron microscopeelectron microscope – uses – uses electrons electrons

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Light microscopeLight microscope

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Carry a Microscope Carry a Microscope CorrectlyCorrectly

Images Produced by Light Images Produced by Light MicroscopesMicroscopes

Amoeba Streptococcus bacteria Anthrax bacteria

Human cheek cells Plant cells Yeast cells

Electron microscopeElectron microscope

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Images Produced by Electron Images Produced by Electron MicroscopesMicroscopes

Cyanobacteria (TEM) Lactobacillus

(SEM)Campylobacter

(SEM) Deinococcus(SEM)

House ant Avian influenza virus Human eyelash Yeast

Electrons – negatively charged particles Electrons – negatively charged particles which orbit the nucleus of an atomwhich orbit the nucleus of an atom

When electrons gain high energy, they When electrons gain high energy, they escape from their orbits. Free electrons escape from their orbits. Free electrons behave like electromagnetic radiationbehave like electromagnetic radiation

Short wavelength (greater energy, Short wavelength (greater energy, shorter wavelength)shorter wavelength)

Advantage of using electrons for Advantage of using electrons for microscopy:microscopy: Wavelength extremely shortWavelength extremely short Negatively charged (can be focused easily Negatively charged (can be focused easily

using electromagnets)using electromagnets)

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Electromagnetic spectrum – whole range of Electromagnetic spectrum – whole range of wavelengthswavelengths

The longer the electromagnetic waves, the lower The longer the electromagnetic waves, the lower their frequencytheir frequency

The greater the energy, the shorter the wavelengthThe greater the energy, the shorter the wavelength The limit of resolution is about ½ the The limit of resolution is about ½ the

wavelength of the radiation used to view the wavelength of the radiation used to view the specimen specimen (if an object is any smaller than half the (if an object is any smaller than half the wavelength of the radiation used to view it, it cannot wavelength of the radiation used to view it, it cannot be seen separately from nearby objects)be seen separately from nearby objects)

Best resolution using microscope that uses visible Best resolution using microscope that uses visible light is 200 nm, since shortest wavelength of visible light is 200 nm, since shortest wavelength of visible light is 400 nm (violet light). Smaller objects can light is 400 nm (violet light). Smaller objects can never be seen using light (ribosomes – 22 nm)never be seen using light (ribosomes – 22 nm)

If an object is transparent it will allow light waves to If an object is transparent it will allow light waves to pass through it and will still not be visiblepass through it and will still not be visible

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The electromagnetic The electromagnetic spectrumspectrum

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Beam of electrons passed Beam of electrons passed throughthrough the specimen before being viewedthe specimen before being viewed

Only electrons that are Only electrons that are transmittedtransmitted (pass through the specimen) are seen(pass through the specimen) are seen

Allows to see thin sections of Allows to see thin sections of specimens (inside the cell)specimens (inside the cell)

Transmission Electron Transmission Electron MicroscopeMicroscope

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Electron beam is used to scan the Electron beam is used to scan the surfacessurfaces of structures and only the of structures and only the reflectedreflected beam beam is observedis observed

Surface structures can be seenSurface structures can be seen

Great depth of field is obtained so that Great depth of field is obtained so that much of the specimen is in focus at the much of the specimen is in focus at the same timesame time

Cannot achieve same resolution as a Cannot achieve same resolution as a transmission electron microscopetransmission electron microscope

Scanning Electron MicroscopeScanning Electron Microscope

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Viewing sample with the electron Viewing sample with the electron microcopemicrocope

Electron beam projected onto a fluorescent Electron beam projected onto a fluorescent screen (areas hit by electrons shine brightly screen (areas hit by electrons shine brightly giving overall a ‘black and white’ picture)giving overall a ‘black and white’ picture)

Stains used to improve contrast contain Stains used to improve contrast contain heavy metal atoms which stop the passage of heavy metal atoms which stop the passage of electronselectrons

Electron beam must be in vacuum to avoid Electron beam must be in vacuum to avoid collision with air moleculescollision with air molecules

Specimen must be dehydrated because water Specimen must be dehydrated because water boils at room temperature in vacuum (only boils at room temperature in vacuum (only dead material can be examined)dead material can be examined)

Great efforts to preserve material in life-like Great efforts to preserve material in life-like state when preparing specimenstate when preparing specimen

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Comparison of advantages and disadvantages of the light and Comparison of advantages and disadvantages of the light and electron microscopeelectron microscope

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LIGHT MICROSCOPELIGHT MICROSCOPE ELECTRON MICROSCOPEELECTRON MICROSCOPE

AdvantagesAdvantages DisadvantagesDisadvantages

Cheap to purchaseCheap to purchase Expensive to purchaseExpensive to purchase

Cheap to operate – uses a little electricity Cheap to operate – uses a little electricity where there is a built-in light sourcewhere there is a built-in light source

Expensive to operate – requires up to 100 Expensive to operate – requires up to 100 000 volts to produce the electric beam000 volts to produce the electric beam

Small and portable Small and portable Very large and must be operated in special Very large and must be operated in special roomsrooms

Unaffected by magnetic fieldsUnaffected by magnetic fields Affected by magnetic fieldsAffected by magnetic fields

Preparation of material is relatively quick Preparation of material is relatively quick and simple, requiring only a little expertiseand simple, requiring only a little expertise

Preparation of material is lengthy and Preparation of material is lengthy and requires considerable expertise and requires considerable expertise and sometimes complex equipmentsometimes complex equipment

Material rarely distorted by preparationMaterial rarely distorted by preparation Preparation of material may distort itPreparation of material may distort it

Living as well as dead material may be Living as well as dead material may be viewedviewed

A high vacuum is required and living A high vacuum is required and living material cannot be observedmaterial cannot be observed

Natural colour of material can be observedNatural colour of material can be observed All images are in black and whiteAll images are in black and white

DisadvantagesDisadvantages AdvantagesAdvantages

Magnifies objects up to 1500XMagnifies objects up to 1500X Magnifies objects over 500 000XMagnifies objects over 500 000X

Can resolve objects up to 200 nm apartCan resolve objects up to 200 nm apart Has a resolving power for biological Has a resolving power for biological specimens of around 1 nmspecimens of around 1 nm

The depth of field is restrictedThe depth of field is restricted It is possible to investigate a greater depth It is possible to investigate a greater depth of fieldof field

GraticuleGraticule

Stage micrometerStage micrometer

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